Amending Clay Soil — Clay Soil Improvement Tips

Heavy clay earth can pose a difficult challenge to any farmer or backyard gardener. Test your soil to find out how suitable it is for planting; if you determine that your soil is overly rich in clay, you can still grow healthy plants. But before you can properly amend a heavy clay soil, it is important to know exactly what a clay-rich soil means.

Sand Silt & Clay

Of the three basic soil types — sand, silt, and clay — clay is actually the most nutrient-rich. If this is true, why do most plants do poorly in clay rich soils? The answer lies in drainage.

Clay has the smallest particle size of all soil types. The materials that make up clay are so small, that water often can not penetrate a layer of clay. On the surface, when exposed to the sun, clay soils often crack and part, allowing some water to seep into the clay, but not allowing it to escape. The end result is that clay soil drainage is slow, and delicate plant roots become starved for oxygen.

Often, they end up rotting in the overly wet environment and the plant fails. On the opposite side of the spectrum, sandy soils with their large particles allow water to quickly pass through the soil hydrating the roots, but also allowing them to receive oxygen. Sand however has few nutrients, so the roots have little to feed on. This in mind, it becomes clear that the way to improve clay rich soil is to increase its ability to drain water.

Common Mistakes When Trying to Improve Clay Soil

The first impulse many people have is to dump some sand in the clay, mix it up, and call it good. They figure the sand will loosen up the soil. This, in fact, will make the soil turn into concrete. With not enough sand, the clay will completely encapsulate the sand particles effectively rendering them useless. For centuries, cultures have been using a mix of clay and sand to create materials like cob and adobe to build their houses. The walls in the picture below were constructed from nothing but clay and sand to give you an idea of how hard this mixture can become!

Good Clay Soil Improvement Techniques

Amending clay soil is a slow and ongoing process. In order to get the job done well, it is best to mix a large quantity of sand, compost, and/or manure into the soil and allow it to break down over time. When selecting sand or manure to use, always select the coarsest variety available. This will make it harder for the clay to completely encapsulate it. Coarse sand is called builders sand, and can be picked up at your local building/landscaping materials yard. For the organic material component, aged kitchen compost or yard waste (often available from your town’s composting facility) work well.

When you have your materials, layer 3-4 inches of sand and 3-4 inches of compost over the entire area you plan to amend. Till this in with a tiller, or turn it in with a shovel to about 12 inches down. Then sprinkle an inch layer of fine sifted compost or a couple inches of straw on top. This is will stop the clay from drying out completely and cracking as the materials slowly mix in.

Your soil should now be ready for planting. Keep in mind that each year following, you should continue to add more organic matter like compost or manure. Over time, your soil can improve to the rich organic loam of all gardener’s dreams.

Do you have more questions? Please leave a comment below.Keep up to date with all the hottest urban planning news by subscribing to our (free) newsletter.

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